Filter For Laminated Circuit Assembly

ABSTRACT

A laminated circuit assembly for filtering signals in one or more signal lines in, for instance, a quantum computing system is provided. In one example, the laminated circuit assembly includes one or more signal lines disposed within a substrate in a first direction. The laminated circuit assembly includes a dielectric portion of the substrate. The laminated circuit assembly includes a filter portion of the substrate extending in a first direction and containing a frequency absorbent material providing less attenuation to a first signal of a first frequency than to a second signal of a second, higher frequency. The filter portion is configured to attenuate infrared signals passing through the one or more signal lines.

PRIORITY CLAIM

The present application claims the benefit of priority of U.S.Provisional Application Ser. No. 63/079,258, filed on Sep. 16, 2020,titled Filter for Laminated Circuit Assembly, which is incorporatedherein by reference.

FIELD

The present disclosure relates generally to laminated circuitassemblies. More particularly, aspects of the present disclosure relateto filters for laminated circuit assemblies.

BACKGROUND

Quantum computing is a computing method that takes advantage of quantumeffects, such as superposition of basis states and entanglement toperform certain computations more efficiently than a classical digitalcomputer. In contrast to a digital computer, which stores andmanipulates information in the form of bits, e.g., a “1” or “0,” quantumcomputing systems can manipulate information using quantum bits(“qubits”). A qubit can refer to a quantum device that enables thesuperposition of multiple states, e.g., data in both the “0” and “1”state, and/or to the superposition of data, itself, in the multiplestates. In accordance with conventional terminology, the superpositionof a “0” and “1” state in a quantum system may be represented, e.g., asa|0>+b|1>. The “0” and “1” states of a digital computer are analogous tothe |0> and |1> basis states, respectively of a qubit.

SUMMARY

Aspects and advantages of embodiments of the present disclosure will beset forth in part in the following description, or can be learned fromthe description, or can be learned through practice of the embodiments.

One example aspect of the present disclosure is directed to a laminatedcircuit assembly. The laminated circuit assembly includes one or moresignal lines disposed within a substrate in a first direction. Thelaminated circuit assembly includes a dielectric portion of thesubstrate. The laminated circuit assembly includes a filter portion ofthe substrate extending in a first direction and containing a frequencyabsorbent material providing less attenuation to a first signal of afirst frequency than to a second signal of a second, higher frequency.The filter portion is configured to attenuate infrared signals passingthrough the one or more signal lines.

Another example aspect of the present disclosure is directed to a methodfor manufacturing a filter for a signal line. The method includesreceiving a laminated circuit assembly having one or more signal linesdisposed in a first direction within a dielectric material of asubstrate, wherein a second direction is normal to the substrate and athird direction is orthogonal to the first direction and the seconddirection. The method includes forming a cavity within the substrate byremoving a portion of the dielectric material above the signal line inthe second direction, the cavity extending in the first direction alongthe signal line. The method includes filling the cavity with a frequencyabsorbent material. The frequency absorbent material provides lessattenuation to a first signal of a first frequency than to a secondsignal of a second, higher frequency. The filled cavity is configured toattenuate infrared signals passing through the one or more signal lines.

Other aspects of the present disclosure are directed to various systems,methods, apparatuses, non-transitory computer-readable media,computer-readable instructions, and computing devices.

These and other features, aspects, and advantages of various embodimentsof the present disclosure will become better understood with referenceto the following description and appended claims. The accompanyingdrawings, which are incorporated in and constitute a part of thisspecification, illustrate example embodiments of the present disclosureand, together with the description, serve to explain the relatedprinciples.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed discussion of embodiments directed to one of ordinary skill inthe art is set forth in the specification, which makes reference to theappended figures, in which:

FIG. 1 depicts an example quantum computing system according to exampleembodiments of the present disclosure;

FIG. 2 depicts an example quantum computing system according to exampleembodiments of the present disclosure;

FIG. 3 depicts an isometric cross-sectional view of an example portionof a laminated circuit assembly according to an example embodiment ofthe present disclosure;

FIG. 4 depicts an isometric cross-sectional view of an example portionof a processed laminated circuit assembly according to an exampleembodiment of the present disclosure;

FIG. 5 depicts an isometric cross-sectional view of an example portionof a processed laminated circuit assembly according to an exampleembodiment of the present disclosure;

FIG. 6 depicts an isometric cross-sectional view of an example portionof a processed laminated circuit assembly according to an exampleembodiment of the present disclosure;

FIG. 7 depicts a cross-sectional view of an example processed laminatedcircuit assembly according to an example embodiment of the presentdisclosure;

FIG. 8 depicts a cross-sectional view of an example processed laminatedcircuit assembly according to another example embodiment of the presentdisclosure;

FIG. 9 depicts a cross-sectional view of an example processed laminatedcircuit assembly according to another example embodiment of the presentdisclosure;

FIG. 10 depicts a cross-sectional view of an example processed laminatedcircuit assembly according to another example embodiment of the presentdisclosure; and

FIG. 11 depicts an example method of manufacturing a laminated circuitassembly according to aspects of example embodiments of the presentdisclosure.

DETAILED DESCRIPTION

Example aspects of the present disclosure are directed to a laminatedcircuit assembly. The circuit assembly can include a signal linedisposed along a substrate. The substrate can include a filter portionthat provides attenuation to signals traveling along the signal line. Insome embodiments, the filter portion can provide different levels ofattenuation based on the frequency of the signal on the signal line. Forinstance, the filter portion can include an absorptive materialconfigured to provide less attenuation to a signal of a first frequencythan to a second signal of a second, higher frequency. In oneembodiment, the filter portion can attenuate signals in an infraredfrequency range.

More particularly, embodiments of a laminated circuit assembly accordingto example aspects of the present disclosure can include a signal lineof any suitable conductive material(s), (e.g., copper, etc.). In someembodiments, the signal line can include a superconducting material,such as a material that is characterized by superconductive propertiesat or below about 10 Kelvin (including example temperatures below about1 Kelvin and/or about 20 milliKelvin). For instance, in one embodiment,the signal line can include niobium. In some embodiments, a signal linemay include one or more superconductive materials in addition to anotherconductive material, such as copper or tin. For instance, asuperconductive material may be coated, covered, and/or otherwiselayered with another conductive material (e.g., deposited and/orelectroplated copper, etc.) to protect the superconductive material,strengthen and/or stiffen the superconductive material portion, and/orotherwise cooperate to form a signal line.

Embodiments of a substrate according to example aspects of the presentdisclosure can include a dielectric material. For instance, thedielectric material can include one or more polymers, one or moreceramics, or composites thereof (e.g., a polymeric matrix with one ormore ceramic fillers). In some embodiments, the dielectric material canbe rigid or substantially rigid. In some embodiments, the dielectricmaterial can include a resilient material (e.g., a flexible material).For instance, one embodiment of a laminated circuit assembly includes aflex circuit board.

As used herein, a “flex circuit board” refers to a board including atleast one generally planar substrate (e.g., layered substrates) or othersupport on which the one or more signal lines are formed or otherwisedisposed and having flexibility in at least one plane. As used herein,“flexibility” refers to a capability of deforming (e.g., subject tomechanical stress, etc.) without breaking. For example, a rectangularflex circuit board may be flexible along a largest surface of therectangular flex circuit board. A rectangular flex circuit board may beflexible and/or rigid along at least a portion of its edges. Theflexibility may be achieved as a property of material(s) from which theflex circuit board and/or layers of the flex circuit board is/are formed(e.g., metals, such as copper, copper alloys, niobium, aluminum, etc.,dielectric materials, nonmetals, polymers, rubbers, etc.), achieved byhinging and/or segmenting of the flex circuit board (e.g., hingingand/or segmenting a rigid portion), and/or in any other suitable manner.The substrate(s) may be strictly planar (e.g., having a substantiallylinear cross-section across a length and width) and/or may be generallyplanar in that the substrate(s) bend, wrinkle, or are otherwisenon-linear in at least one cross-section but generally represent a shapehaving a depth significantly less than (e.g., less than about 10% of) alength and width.

In some embodiments, one or more layers of dielectric material can belaminated together to sandwich one or more signal lines therebetween toform the substrate with the signal line(s) embedded therein. However, ingeneral, it is contemplated that the signal line(s) can be disposedalong one or more surfaces of a substrate (e.g., an exterior surface,such as in a microstrip implementation) and/or within the substrateaccording to any suitable construction method.

Embodiments of a substrate according to example aspects of the presentdisclosure can include a filter material. In some embodiments, a filtermaterial can be distributed and/or embedded within the dielectricmaterial. For instance, a polymeric dielectric material can be dopedwith a filter material (e.g., magnetically loaded with frequencyabsorbing particles). In this manner, the dielectric portion of thesubstrate and the filter portion of the substrate coincide, as thedielectric portion can be a portion that provides filtering effects.

In some embodiments, however, a filter portion can include differentmaterial(s) than some other portions of the substrate, such as thedielectric portion. For instance, a filter portion of the substrate caninclude a portion of dielectric material (e.g., optionally the samedielectric material) that includes a greater concentration of frequencyabsorbing components (e.g., frequency absorbing particles) than anotherportion of the same or different dielectric material (e.g., which maycontain none). It is contemplated that, for instance, additivemanufacturing techniques may be applied to selectively position materialcomprising absorptive components within a larger portion of material nototherwise comprising the absorptive components.

In some examples, the filter material can provide less attenuation tosignals of a first frequency and greater attenuation to signals of asecond, higher frequency. For instance, some filter materials provideattenuation that increases in a substantially monotonic fashion withincreasing signal frequency for at least a portion of a targetedfrequency band. In some embodiments, aspects of the filter material canbe configured for lowpass and/or bandpass operation.

In some embodiments, the filter portion of the substrate can be boundedby one or more boundaries of a cavity within the substrate (e.g., acavity within the dielectric material). For instance, a cavity withinthe substrate can be filled with a filter material (e.g., a magneticallyloaded polymer). In some embodiments, the cavity can be filled (e.g.,partially or completely) with filter material via an access within thesubstrate when the filter material is in any pourable, injectable,and/or moldable state (e.g., flowing particulates, soft/plasticizedmaterials, gels, slurries, pastes, foams, uncured thermosets,softened/melted thermoplastics, etc.). In some embodiments, the cavitycan be filled with the filter material in a substantially solid state(e.g., by press-fitting into the cavity, etc.).

In some embodiments, the cavity can radially surround or otherwiseencompass at least one portion of the signal line. For instance, thesignal line can extend in a first direction in the substrate. A seconddirection can be defined in a direction normal to an outer surface ofthe substrate (e.g., in the direction of a thickness of the substrate).A third direction can be defined orthogonal to the first and seconddirections. In general, the dimensions of the cavity in the first,second, and third directions can be configured to cause the desiredfiltration of the signals on the signal line when the cavity is filledwith a filtering material. For instance, in one embodiment, the lengthof the cavity in the first direction can be extended to increase theattenuation of the filter for a given signal frequency. For instance, inone embodiment, a filter material can provide linearly increasingattenuation having a slope of at least about 0.5 dB/GHz. In addition toa length extending in the first direction, the cavity can extend abovethe signal line in the second direction and/or beside the signal line inthe third direction.

In some embodiments, one or more conductors may be laminated to thesubstrate. For instance, a planar conductor may be laminated to onesurface of the substrate, and, in some embodiments, another planarconductor may be laminated to an opposing surface of the substrate. Forexample, a substrate, a signal line, and one or more planar conductorscan be arranged into a microstrip or stripline configuration. In someembodiments, a conductor can be applied over one or more accesses in thesubstrate used to fill a cavity with filter material. For instance, aplanar conductor can be laminated over the access(es), optionallyoverlapping one or more other planar conductors. In some embodiments, aconductive material can be sprayed, spread, deposited, and/or otherwiseapplied over the access(es). For instance, conductive material(s) caninclude a curable nonmetallic matrix that is applied in an uncuredstate.

Example aspects of the present disclosure are also directed to methodsfor manufacturing a laminated circuit assembly. For instance, alaminated circuit assembly including one or more signal lines disposedin a first direction within a dielectric material of a substrate can bereceived or otherwise selected for processing. In one embodiment, acavity can be formed within the substrate. For instance, the cavity canbe formed by removing a portion of the dielectric material within thesubstrate. Material can be removed in any suitable fashion, includingablation, abrasion, cutting, and the like. Once formed, the cavity canbe filled with a frequency absorbent material. In some embodiments, thecavity can be filled with the frequency absorbent material while thedielectric material (e.g., polymer) is in an uncured state.

For example, the frequency absorbent material can provide lessattenuation to a first signal of a first frequency than to a secondsignal of a second, higher frequency (e.g., as described herein). Insome embodiments, the filled cavity may be configured to attenuateinfrared signals passing through the one or more signal lines.

In some embodiments, a first signal line can have a first filter portioncorresponding thereto; and a second adjacent signal line can have asecond filter portion corresponding thereto. The first filter portionand the second filter portion are offset from each other in a firstdirection.

Example aspects of the present disclosure are also directed to cryostatsincluding the circuit assemblies described herein. For instance, acryostat can include one or more cooling stages for cooling one or morecomponents of a computing system. In one embodiment, a stage can beconfigured to cool a portion of the computing system to about 20milliKelvin or less. One or more signal lines coupling a control unit tothe cooled portion of the computing system can be part of a circuitassembly as disclosed herein, comprising a filter portion as disclosedherein.

Aspects of the present disclosure provide a number of technical effectsand benefits. For instance, circuit assemblies, systems, and methodsaccording to aspects of the present disclosure provide improvedcommunication of sensitive signals. For instance, in some embodiments, aplurality of signals (e.g., control and/or other interfacing signals)are communicated on a signal line of a circuit assembly according to thepresent disclosure. For example, a first signal can have a firstfrequency less than about 500 MHz and a second signal can have a secondfrequency greater than about 2 GHz and less than about 8 GHz. Thecircuit assemblies according to example embodiments of the presentdisclosure can be configured to contain frequency absorbent materialproviding greater attenuation to the second signal than to the firstsignal. In this manner, the attenuation applied to each set ofinterfacing signals can be configured for the desired operationalcharacteristics. Of further advantage, circuit assemblies according toexample embodiments of the present disclosure can be configured toprovide greater attenuation to infrared signals than is provided toeither the first signal or the second signal. For instance, in someembodiments, infrared signals can disrupt communication and/or increasethermal loading on connected components.

Of further advantage, circuit assemblies, systems, and methods accordingto aspects of the present disclosure provide for improvedmanufacturability. For instance, embodiments of the present disclosurecan provide for high-performance circuit assemblies which can bemanufactured at a low cost and high yield.

Of further advantage, circuit assemblies, systems, and methods accordingto aspects of the present disclosure provide for compact and scalableimplementations of filtered signal lines. For instance, someimplementations are sensitive to signal interference (e.g., qubitinterface signals), and prior approaches to filtering and isolatingsignal lines for qubit interfacing have not provided suitably compactconfigurations for scaling the number of qubits in a quantum computingsystem.

With reference again to the FIGS., additional example embodiments ofsystems and methods the present disclosure will be discussed in furtherdetail. The use of the term “about” in conjunction with a numericalvalue refers to within 10% of the stated amount.

FIG. 1 depicts an example quantum computing system 50. The examplesystem 50 is an example of a system implemented as a classical orquantum computer program on one or more classical computers or quantumcomputing devices in one or more locations, in which the systems,components, and techniques described below can be implemented. FIG. 1depicts an example quantum computing system that can be used toimplement aspects of the present disclosure. Those of ordinary skill inthe art, using the disclosures provided herein, will understand thatother quantum computing structures or systems can be used withoutdeviating from the scope of the present disclosure.

The system 50 includes quantum hardware 52 in data communication withone or more classical processor(s) 54. For instance, quantum hardware 52can represent and/or manipulate information using qubits. A qubit can beor include any suitable quantum device that enables the superposition ofmultiple states, (e.g., data in both the “0” and “1” state). As oneexample, a qubit can be or include a unit of superconducting material,such as superconducting material that achieves superconductivity intemperatures below about 10 mK.

The quantum hardware 52 can include components for performing quantumcomputation. For example, the quantum hardware 52 can include a quantumsystem 60, control device(s) 62, and readout device(s) 64 (e.g., readoutresonator(s)). The quantum system 60 can include one or more multi-levelquantum subsystems, such as a register of qubits. In someimplementations, the multi-level quantum subsystems can includesuperconducting qubits, such as flux qubits, charge qubits, transmonqubits, gmon qubits, etc.

The classical processor(s) 54 can be binary processors, such asprocessors that operate on data represented as a plurality of bits. Asone example, bits can be represented by a voltage differential between alow voltage (e.g., 0V) and a high voltage (e.g., 5V) at a point ofreference, such as a memory cell, circuit node, etc. The low voltage canbe associated with a “0” state and the high voltage can be associatedwith a “1” state. The classical processor(s) 54 can be configured to, inaddition to any other suitable function(s) of the classical processor(s)54, control the quantum hardware 52. For instance, the classicalprocessor(s) 54 can be coupled to the quantum hardware 52 (e.g., bysignal lines) and/or configured to send control signals to performquantum operations using the quantum hardware 52. As one example, theclassical processor(s) 54 can be configured to send control signals thatimplement quantum gate operations at the quantum hardware 52 (e.g., bycontrol device(s) 62). Additionally and/or alternatively, the classicalprocessor(s) 54 can be configured to send control signals that cause thequantum hardware 52 to perform quantum state measurements and/or providethe quantum state measurements to the classical processor(s) 54 (e.g.,by readout device(s) 64). For example, the classical processor(s) 54 canreceive measurements of the quantum system 60 that can be interpretableby the classical processor(s) 54.

The type of multi-level quantum subsystems that the system 50 utilizesmay vary. For example, in some cases it may be convenient to include oneor more readout device(s) 64 attached to one or more superconductingqubits (e.g., transmon, flux, gmon, xmon, or other qubits).

Quantum circuits may be constructed and applied to the register ofqubits included in the quantum system 60 via multiple signal lines thatare coupled to one or more control devices 62. Example control devices62 that operate on the register of qubits can be used to implementquantum logic gates or circuits of quantum logic gates (e.g., Hadamardgates, controlled-NOT (CNOT) gates, controlled-phase gates, T gates,multi-qubit quantum gates, coupler quantum gates, etc). The one or morecontrol devices 62 may be configured to operate on the quantum system 60through one or more respective control parameters (e.g., one or morephysical control parameters). For example, in some implementations, themulti-level quantum subsystems may be superconducting qubits and thecontrol devices 62 may be configured to provide control pulses tocontrol lines (e.g., signal lines 120) to generate magnetic fields toadjust a frequency of the qubits.

The quantum hardware 52 may further include readout devices 64 (e.g.,readout resonators). Measurement results 58 obtained via measurementdevices may be provided to the classical processors 54 for processingand analyzing. In some implementations, the quantum hardware 52 mayinclude a quantum circuit and the control device(s) 62 and readoutdevices(s) 64 may implement one or more quantum logic gates that operateon the quantum system 60 through physical control parameters (e.g.,microwave pulse) that are sent through wires included in the quantumhardware 52. Further examples of control devices include arbitrarywaveform generators, wherein a DAC creates the signal.

The readout device(s) 64 may be configured to perform quantummeasurements on the quantum system 60 and send (e.g., by signal lines120) measurement results 58 to the classical processors 54. In addition,the quantum hardware 52 may be configured to receive data (e.g., bysignal lines 120) specifying physical control parameter values 56 fromthe classical processors 54. The quantum hardware 52 may use thereceived physical control parameter values 56 to update the action ofthe control device(s) 62 and readout devices(s) 64 on the quantum system60. For example, the quantum hardware 52 may receive data specifying newvalues representing voltage strengths of one or more DACs included inthe control devices 62 and may update the action of the DACs on thequantum system 60 accordingly. The classical processors 54 may beconfigured to initialize the quantum system 60 in an initial quantumstate, e.g., by sending data to the quantum hardware 52 specifying aninitial set of parameters 56.

The readout device(s) 64 can take advantage of a difference in theimpedance for the |0> and |1> states of an element of the quantumsystem, such as a qubit, to measure the state of the element (e.g., thequbit). For example, the resonance frequency of a readout resonator cantake on different values when a qubit is in the state |0> or the state|1>, due to the nonlinearity of the qubit. Therefore, a microwave pulsereflected from the readout device 64 carries an amplitude and phaseshift that depend on the qubit state. In some implementations, a Purcellfilter can be used in conjunction with the readout device(s) 64 toimpede microwave propagation at the qubit frequency.

The system 50 includes control device(s) 62. Control device(s) 62 canoperate the quantum hardware 52. For example, control device(s) 62 caninclude a waveform generator configured to generate control pulsesaccording to example aspects of the present disclosure.

In some implementations, the control device(s) 62 may include a dataprocessing apparatus and associated memory. The memory may include acomputer program having instructions that, when executed by the dataprocessing apparatus, cause the data processing apparatus to perform oneor more functions described herein.

FIG. 2 depicts an example quantum computing system 300 according toexample embodiments of the present disclosure. The quantum computingsystem 300 can include one or more classical processors 302 and quantumhardware 304 including one or more qubits. The quantum computing system300 can include a chamber mount 308 configured to support the quantumhardware 304 and a vacuum chamber configured to receive the chambermount 308 and dispose the quantum hardware 304 in a vacuum. The vacuumchamber can form a cooling gradient from an end of the vacuum chamber(e.g., cap 307) to the quantum hardware 304. For example, the vacuumchamber can form a cooling gradient from a first temperature, such asroom temperature (e.g., about 300 Kelvin) to a second temperature, suchas at or about absolute zero (e.g., less than about 1 Kelvin), such asto provide a temperature at the quantum hardware 304 at which the qubitsexperience superconductivity. In some embodiments, the cooling gradientcan be formed by a plurality of cooling stages having progressivelyincreasing and/or decreasing temperatures. As one example, the coolingstages can be stages of a staged cryogenic cooling system, such as adilution refrigerator.

The quantum computing system 300 can include one or more signal linesbetween the classical processor(s) 302 and quantum hardware 304.According to example aspects of the present disclosure, the quantumcomputing system 300 can include one or more flex circuit boards 306including one or more signal lines. The flex circuit board(s) 306 can beconfigured to transmit signals by the one or more signal lines throughthe vacuum chamber to couple the one or more classical processors 302 tothe quantum hardware 304. The flex circuit board(s) 306 can include aplurality of signal lines and can provide a significantly improvedsignal line density, in addition to providing improved isolation,reduced thermal conductivity, and/or improved scalability. For instance,including flex circuit boards 306 according to example aspects of thepresent disclosure to couple the classical processors 302 to the quantumhardware 304 can provide for infrastructure that reliably scales to theincreasingly greater numbers of qubits that are achieved and/or expectedin contemporary and/or future quantum computing systems.

In some embodiments, some or all of the flex circuit board(s) 306 caninclude at least one ground layer. The ground layer can form an outersurface of the flex circuit board 306, such as an outer surface alongthe largest surface. In some embodiments, the flex circuit board 306 caninclude two ground layers, such as two parallel and spaced apart groundlayers. For instance, the two ground layers can form both largest outersurfaces of the flex circuit board 306. A ground layer can act as anelectrical isolation layer to isolate signal lines on one side of theground layer from interfering signals (e.g., from signal lines on otherlayers, other boards, the environment, etc.) on another side of theground layer. For instance, the ground layer can be coupled to earthground and/or other suitable ground(s) or reference.

The ground layer(s) can be or can include any suitable electricallyconductive material. In some embodiments, the ground layer(s) can be orcan include superconducting ground layer(s) including superconductingmaterial(s), such as superconducting material(s) that achieve(s)superconductivity at a temperature less than about 3 Kelvin, such asless than about 1 Kelvin, such as less than about 20 milliKelvin. Asexamples, the ground layer(s) can be or can include niobium, tin,aluminum, molybdenum disulfide, BSCCO, and/or other suitablesuperconducting materials. Additionally and/or alternatively, the groundlayer(s) can be or can include material having high signal transferperformance characteristics, such as low resistance, low reflectivity,low distortion, etc. such that a signal is substantially unchanged bypassing through the signal line. As examples, the ground layer(s) can beor can include copper, gold, and/or other suitable materials having highsignal transfer performance characteristics. Additionally and/oralternatively, the ground layer(s) can be or can include material(s)having desirable thermal characteristics, such as suitably high and/orlow thermal transfer, such as, for example, copper, copper alloy, thinsuperconducting materials, etc.

In some embodiments, the flex circuit board 306 can include at least onedielectric layer. The dielectric layer(s) can be or can include anysuitable dielectric material, such as dielectric polymers. In someembodiments, the dielectric layer(s) can be or can include flexibledielectric material. As one example, the dielectric layer(s) can be orcan include polyimide. At least a portion of the dielectric layer(s) canbe formed on or otherwise disposed proximate to at least a portion of aninner surface of the ground layer(s). For example, in some embodiments,an inner surface of a ground layer can be mated with an outer surface ofa dielectric layer. Furthermore, in some embodiments, inner surfaces oftwo dielectric layers can be mated with signal lines disposedtherebetween.

The flex circuit board 306 can include one or more signal lines. The oneor more signal lines can be disposed on a surface (e.g., an innersurface) of at least one dielectric layer. As an example, in someimplementations, the one or more signal lines can be disposed betweenopposing inner surfaces of two dielectric layers. The signal line(s) canbe or can include any suitable electrically conductive material. In someembodiments, the signal line(s) can be or can include superconductingsignal line(s) including superconducting material(s), such assuperconducting material(s) that achieve(s) superconductivity at atemperature less than about 3 degrees Kelvin, such as less than about 1degree Kelvin, such as less than about 20 milliKelvin. As examples, thesignal line(s) can be or can include niobium, tin, aluminum, molybdenumdisulfide, BSCCO, and/or other suitable superconducting materials.Additionally and/or alternatively, the signal line(s) can be or caninclude material having high signal transfer performancecharacteristics. As examples, the signal line(s) can be or can includecopper, gold, and/or other suitable materials having high signaltransfer performance characteristics. Additionally and/or alternatively,the signal line(s) can be or can include material(s) having desirablethermal characteristics, such as, for example, copper, copper alloy,thin superconducting material, etc.

In some embodiments, the flex circuit board 306 can include one or morevias. For instance, the vias can extend through the ground layer(s), thedielectric layer(s), and/or the signal line(s). The vias can serve toimprove isolation of the signal lines. Additionally and/oralternatively, the vias can serve to couple multiple ground layersand/or transfer signals between layers of the flex circuit board. Insome embodiments, the via(s) can be plated with via plate(s) that extendalong the via(s). In some embodiments, the via plate(s) can be or caninclude conductive material, such as copper.

For instance, in some embodiments, a quantum computing system 300 caninclude quantum hardware 304 in data communication with one or moreclassical processor(s) 302. For instance, quantum hardware 304 canrepresent and/or manipulate information using qubits. A qubit can be orinclude any suitable quantum device that enables the superposition ofmultiple states, e.g., both the “0” and “1” state. As one example, aqubit can be or include a unit of superconducting material, such assuperconducting material that achieves superconductivity at atemperature of less than about 3 degrees Kelvin, such as less than about1 degree Kelvin, such as less than about 20 milliKelvin. In someembodiments, the quantum computing system 300 can include one or moremulti-level quantum subsystems, such as a register of qubits. In someimplementations, the multi-level quantum subsystems can includesuperconducting qubits, such as flux qubits, charge qubits, transmonqubits, gmon qubits, etc.

The classical processor(s) 302 can be binary processors, such asprocessors that operate on data represented as a plurality of bits. Asone example, bits can be represented by a voltage differential between alow voltage (e.g., 0V) and a high voltage (e.g., 5V) at a point ofreference, such as a memory cell, circuit node, etc. The low voltage canbe associated with a “0” state and the high voltage can be associatedwith a “1” state. The classical processor(s) 302 can be configured to,in addition to any other suitable function(s) of the classicalprocessor(s) 302, control the quantum hardware 304. For instance, theclassical processor(s) 302 can be coupled to the quantum hardware 304(e.g., by signal lines included in flex circuit boards 306 according toexample aspects of the present disclosure) and/or configured to sendcontrol signals to perform quantum operations using the quantum hardware304. As one example, the classical processor(s) 302 can be configured tosend control signals that implement quantum gate operations at thequantum hardware 304 (e.g., by control device(s)). Additionally and/oralternatively, the classical processor(s) 302 can be configured to sendcontrol signals that cause the quantum hardware 304 to perform quantumstate measurements and/or provide the quantum state measurements to theclassical processor(s) 302 (e.g., by readout device(s)). For example,the classical processor(s) 302 can receive measurements of the quantumsystem that can be interpretable by the classical processor(s) 302.

According to example aspects of the present disclosure, the quantumcomputing system 300 can include one or more flex circuit boards 306including one or more signal lines. The classical processor(s) 302 canbe coupled to at least one first flex circuit board. For instance, theclassical processor(s) 302 can be coupled to the first flex circuitboard(s) 314 by a classical-flex interconnect 332. The classical-flexinterconnect 332 can convert from a classical signal transmission medium(e.g., a coaxial cable) 312 to the first flex circuit board(s) 314.

As one example, the classical-flex interconnect 332 can be or caninclude a compression interposer. The compression interposer can includean array (e.g., a two-dimensional array) of spring pads. A connectorreceiving signals from the classical processor(s) 302, such as via oneor more coaxial cables 312 (e.g., one coaxial cable 312 per signal line)can be compressed against the compression interposer to form signalcommunications between the spring pads and the connector (e.g., thecoaxial cables). The spring pads can each be coupled to a signal line onthe first flex circuit board 314 such that signals can be transmittedfrom the classical processor(s) 302 (e.g., the coaxial cables) to thesignal lines. The compression interposer can provide for connectingsignal transmission media 312 having a relatively lower spatial density,such as coaxial cables, which may occupy a relatively larger amount ofspace per cable, to signal transmission media having a relatively higherspatial density, such as signal lines embedded in a first flex circuitboard 314 provided according to example aspects of the presentdisclosure. Additionally, the compression interposer can achieve highisolation between signal lines and/or low reflectivity along a signalline that is/are suitable for quantum computing applications.

In some embodiments, the first flex circuit board(s) 314 can be or caninclude a first flex circuit board material at the ground layer(s)and/or the signal line(s). The first flex circuit board material can beselected to provide high signal transfer performance characteristics. Asexamples, the first flex circuit board material can be or can includecopper, brass, gold, and/or other suitable materials having high signaltransfer performance characteristics. For instance, the first flexcircuit board(s) 314 can include copper signal lines and/or groundlayer(s) to provide high signal transfer performance characteristics.

The first flex circuit board(s) 314 can pass through a hermetic seal 352positioned at an end (e.g., an entrance) of the vacuum chamber, such ascap 307. For example, a flex circuit board (e.g., first flex circuitboard 314) can be configured to pass through the hermetic seal 352 suchthat a first portion of the flex circuit board (e.g., first flex circuitboard 314) is disposed in the vacuum chamber and a second portion of theflex circuit board (e.g., first flex circuit board 314) is disposedoutside of the vacuum chamber while the hermetic seal 352 forms a vacuumseal for the vacuum chamber. The hermetic seal 352 can provide for thefirst flex circuit board(s) 314 to enter the vacuum chamber without(e.g., substantially) destroying a vacuum created by the vacuum chamber.As one example, the hermetic seal 352 can include a fitted seal for eachfirst flex circuit board 314. The fitted seal(s) can receive the firstflex circuit board(s) 314 and form a vacuum seal with surface(s) of thefirst flex circuit board(s) 314. Additionally, the hermetic seal 352 caninclude one or more seal slots configured to receive the fitted seal(s)and/or the first flex circuit board(s) 314. For example, the fittedseal(s) can form a vacuum seal with the seal slot(s) while allowing thefirst flex circuit board(s) 314 to pass through the seal slot(s) andinto the vacuum chamber. In this way, the flex circuit board(s) 306 canenter the vacuum chamber without experiencing signal disruptions frombreaks in the circuit boards, as the boards can continuously pass intothe vacuum chamber. In some embodiments, the hermetic seal 352 caninclude fastening systems to secure the fitted seals to the seal slotsand/or form a vacuum seal, such as, for example, screws, bolts, sealrings, O rings, etc. In some embodiments, the hermetic seal 352 can forma vacuum seal without requiring adhesive material (e.g., glue, resin,etc.) such that, for example, residual adhesive material does notcontaminate the flex circuit boards 306.

The first flex circuit board(s) 314 can be coupled to at least onesecond flex circuit board(s) 316. The first flex circuit board(s) 314can be coupled to the second flex circuit board(s) 316 by at least oneflex-flex interconnect 334. For instance, the flex-flex interconnect(s)334 can couple (structurally and/or electrically) the ground layer(s),dielectric layer(s), and/or signal line(s) of a first flex circuit board314 to a second flex circuit board 316. As examples, the flex-flexinterconnect(s) 334 can be formed by soldering, welding, and/orotherwise fusing components of a first flex circuit board 314 to asecond flex circuit board 316. The flex-flex interconnect(s) 334 can beor can include any suitable interconnection of two flex circuit board(s)306 such as, for example, a butt joint, an overlap joint, and/or anyother suitable interconnection(s).

The second flex circuit board(s) 316 can have at least a differentmaterial composition from the first flex circuit board(s) 314. In someembodiments, the second flex circuit board(s) 316 can be or can includea second flex circuit board material at the ground layer(s) and/or thesignal line(s). The second flex circuit board material can be selectedto provide high signal transfer performance characteristics and/orreduced thermal conductivity. As examples, the second flex circuit boardmaterial can be or can include a copper alloy and/or other suitablematerials having desirable thermal characteristics. For instance, thesecond flex circuit board(s) 316 can include copper alloy signal linesand/or ground layer(s) to provide reduced thermal conductivity from theupper portions of the vacuum chamber (e.g., first circuit boards 314)and/or dispelling heat produced at subsequent components, such assurface mount attenuators 354.

In some embodiments, the second flex circuit board(s) 316 can be coupledto at least one surface mount attenuator board 318. For instance, thesecond flex circuit board(s) 316 can be coupled to the surface mountattenuator board(s) 318 by at least one flex-flex interconnect 336. Forinstance, the flex-flex interconnect(s) 336 can couple (structurallyand/or electrically) the ground layer(s), dielectric layer(s), and/orsignal line(s) of a second flex circuit board 316 to a surface mountattenuator board 318. As examples, the flex-flex interconnect(s) 336 canbe formed by soldering, welding, and/or otherwise fusing components of asecond flex circuit board 316 to a surface mount attenuator board 318.The flex-flex interconnect(s) 336 can be or can include any suitableinterconnection of two flex circuit board(s) 306 such as, for example, abutt joint, an overlap joint, and/or any other suitableinterconnection(s).

The surface mount attenuator board 318 can be a flexible printed circuitboard. In some embodiments, the surface mount attenuator board(s) 318can be or can include a surface mount attenuator board material at theground layer(s) and/or the signal line(s). The surface mount attenuatorboard material can be selected to provide high signal transferperformance characteristics. As examples, the surface mount attenuatorboard material can be or can include copper, brass, gold, and/or othersuitable materials having high signal transfer performancecharacteristics. For instance, the surface mount attenuator board caninclude copper signal lines and/or ground layer(s) to provide highsignal transfer performance characteristics.

The surface mount attenuator board(s) 318 can include one or moresurface mount attenuators 354. The surface mount attenuator(s) 354 canbe configured to attenuate or block thermal photon interference. In someembodiments, the surface mount attenuator board(s) 318 and/or thesurface mount attenuator(s) 354 can be placed at a temperature coldenough such that the surface mount attenuator(s) 354 do not producethermal photons. In some embodiments, the surface mount attenuator(s)354 can be disposed in an isolation plate. The isolation plate can beconfigured to isolate the one or more surface mount attenuators. Theisolation plate can be attached to the surface mount attenuator board(s)318. In some embodiments, the isolate plate can be mounted to a groundlayer and/or grounded. The isolation plate can include one or morecavities configured to isolate a first surface mount attenuator from asecond surface mount attenuator. For example, the cavities can surroundthe first surface mount attenuator in a direction of a second surfacemount attenuator and block cross-talk between attenuators.

The quantum computing system 300 can include at least one third flexcircuit board 320. For instance, the surface mount attenuator board(s)318 can be coupled to the third flex circuit board(s) 320 by at leastone flex-flex interconnect 338. For instance, the flex-flexinterconnect(s) 338 can couple (structurally and/or electrically) theground layer(s), dielectric layer(s), and/or signal line(s) of a surfacemount attenuator board 318 to a third flex circuit board 320. Asexamples, the flex-flex interconnect(s) 338 can be formed by soldering,welding, and/or otherwise fusing components of a surface mountattenuator board 318 to a third flex circuit board 320. The flex-flexinterconnect(s) 338 can be or can include any suitable interconnectionof two flex circuit board(s) 306 such as, for example, a butt joint, anoverlap joint, and/or any other suitable interconnection(s).

The third flex circuit board(s) 320 can be positioned at a point in thevacuum chamber at which the cooling gradient is cool enough such thatsome materials exhibit superconductivity. For example, at least aportion of the third flex circuit board(s) 320 can have a temperature ofless than about 3 degrees Kelvin.

In some embodiments, the third flex circuit board(s) 320 can be or caninclude a third flex circuit board material at the ground layer(s)and/or the signal line(s). The third flex circuit board(s) 320 materialcan be selected to be superconducting at a temperature which at least aportion of the third flex circuit board(s) 320 experiencessuperconductivity. As examples, the third flex circuit board(s) 320material can be or can include niobium, tin, aluminum, and/or othersuitable superconducting materials. For instance, the third flex circuitboard(s) 320 can include copper-plated niobium signal lines and/orground layer(s) to provide superconductivity. For instance, the copperplating on the copper-plated niobium board(s) can be useful ininterfacing with the superconducting niobium, which can provide forimproved signal transfer characteristics. In some embodiments, thecopper-plated niobium board(s) can be formed by first applying a layerof niobium, followed by a thin layer of copper to prevent the formationof oxides, then a thicker layer of copper.

In some embodiments, the third flex circuit board(s) 320 can be coupledto at least one fourth flex circuit board 322. The third flex circuitboard(s) 320 can be coupled to the fourth flex circuit board(s) 322 byat least one flex-flex interconnect 340. For instance, the flex-flexinterconnect(s) 340 can couple (structurally and/or electrically) theground layer(s), dielectric layer(s), and/or signal line(s) of a thirdflex circuit board 320 to a fourth flex circuit board 322. As examples,the flex-flex interconnect(s) 340 can be formed by soldering, welding,and/or otherwise fusing components of a third flex circuit board 320 toa fourth flex circuit board 322. The flex-flex interconnect(s) 340 canbe or can include any suitable interconnection of two flex circuitboard(s) 306 such as, for example, a butt joint, an overlap joint,and/or any other suitable interconnection(s).

The fourth flex circuit board(s) 322 can couple the third flex circuitboard(s) 320 to the quantum hardware 304. For example, a connector 342at an end of the fourth flex circuit board(s) 322 can attach to a portthat is in signal communication with the quantum hardware 304. As oneexample, the connector can be a T-joint connector, such as a T-jointconnector including superconducting materials (e.g., tin). Additionallyand/or alternatively, the connector 342 may be a planar spring array.

In some embodiments, the fourth flex circuit board(s) 322 can be or caninclude a fourth flex circuit board material at the ground layer(s)and/or the signal line(s). The fourth flex circuit board(s) 322 materialcan be selected to provide high signal transfer performancecharacteristics. As examples, the fourth flex circuit board(s) 322material can be or can include copper, brass, gold, and/or othersuitable materials having high signal transfer performancecharacteristics. For instance, the fourth flex circuit board(s) 322 caninclude copper signal lines and/or ground layer(s) to provide highsignal transfer performance characteristics. Additionally and/oralternatively, the fourth flex circuit board(s) 322 material can beselected to be superconducting at temperatures which at least a portionof the fourth flex circuit board(s) 322 experience. As examples, thefourth flex circuit board(s) 322 material can be or can include niobium,tin, aluminum, and/or other suitable superconducting materials.

According to example aspects of the present disclosure, the fourth flexcircuit board(s) 322 can be or can include a filter 356, such as an XYZand/or IR filter 356. The filter 356 can include the laminated circuitassembly according to any of the embodiments described herein. Forinstance, the filter 356 can be configured to reduce effects of noise,thermal photons, and/or other potential sources of interference. As oneexample, the filter 356 can include a cavity in the fourth flex circuitboard(s) 322 that is filled with a filter material, such as aparticulate suspension, to provide XYZ/IR filtering. In some examples,the filter material can provide less attenuation to signals of a firstfrequency and greater attenuation to signals of a second, higherfrequency. For instance, some filter materials provide attenuation thatincreases in a substantially monotonic fashion with increasing signalfrequency for at least a portion of a targeted frequency band. In someembodiments, aspects of the filter material can be configured forlowpass and/or bandpass operation.

FIG. 3 depicts an example laminated circuit assembly that can be used toimplement a filter according to example embodiments of the presentdisclosure. The laminated circuit assembly 100 comprises a signal line102 within a substrate 104. In the embodiment depicted, planarconductors 106 a and 106 b are laminated to the upper and lower surfacesof the substrate 104, respectively, but it is contemplated that any oneof planar conductors 106 a and 106 b could be substituted with otherconductor geometries and/or omitted. For instance, the embodimentdepicted in FIG. 3 can correspond to a “stripline” configuration, withthe signal line 102 comprising a conductive trace running in thex-direction between two parallel planar conductors, but systems andmethods of the present disclosure can comprise embodiments with othercircuit configurations, including “microstrip” configurations andsubstantially any configuration of one or more conductors 102 (which canbe traces, wires, etc.) and a substrate 104 (e.g., circuit boardsgenerally, such as single layer, double layer, and/or multilayer printedcircuit boards).

In some embodiments, the signal line 102 can comprise one or moreconductive materials (e.g., copper, gold, silver, aluminum, tin, zinc,niobium, palladium, platinum, titanium, tungsten, vanadium, magnesium,molybdenum, magnesium diboride, etc.) which have been formed into aconductive body, such as a strip or trace. For instance, the signal line102 can comprise multiple conductive materials in an alloy and/orcomposite formulation.

In some embodiments, the signal line 102 can comprise a plurality oflayers of conductive material(s). In one example, the signal line 102can comprise at least one layer of a superconducting material (e.g.,superconducting at temperatures less than about 3 degrees Kelvin, suchas less than about 1 degree Kelvin, such as less than about 20milliKelvin, such as niobium). In some embodiments, the superconductingmaterial can be layered with another conductor. For instance, asuperconducting layer can be deposited on a surface of a substrate, suchas by vacuum deposition, and another layer (e.g., a copper layer, a tinlayer, etc.) can be deposited onto the surface of the superconductingconductor. In some embodiments, the other layer can be deposited ontothe superconducting layer to provide protection to the superconductinglayer (e.g., from oxidation). For instance, a first deposition candeposit superconducting material onto a substrate in a vacuumenvironment, and, without releasing the vacuum, a second deposition candeposit another conductor to shield the superconducting material fromthe atmosphere. In some embodiments, one or more additional layers ofconductive material (e.g., the same or different conductive material)can be plated on top of the deposited layers. For instance, the seconddeposition can provide a thin protective coating for the superconductor,and a subsequent plating (e.g., electroplating) can provide a thickerconductive layer. In some example aspects, a thicker, plated conductivelayer can provide structural support to improve the strength and/orresilience of the superconductive layer(s) of the signal line 102. Insome embodiments, one or more of planar conductors 106 a and 106 b (andany plated vias associated therewith) can be fashioned similarly usingone or more deposited layers and one or more plated layers.

In some embodiments, a signal line 102 can be deposited or otherwiselaminated on a substrate. In some embodiments, a signal line 102 can beembedded within a substrate. For instance, one or more layers of apolymeric substrate can be fused or otherwise joined, such that anysignal lines 102 on a surface of one of the layers can be embeddedwithin the whole substrate. One example is shown in FIG. 3, with signalline 102 embedded within substrate 104 and extending in the x-direction.

In some embodiments, the substrate 104 can comprise one or morepolymers. In some implementations, the substrate 104 can comprise areinforced polymer, such as a fiber-reinforced polymer (e.g.,fiberglass). In some embodiments, the substrate 104 can comprise afilled polymer. In some embodiments, the substrate can be loaded with afiller comprising frequency absorbing particles.

In some embodiments, the substrate 104 can comprise a filter portion.For instance, a portion of the substrate 104 can comprise a filter forfiltering signals traveling along the signal line 102 (e.g., along atransmission line comprising signal line 102 and/or planar conductors106 a and 106 b, if present). The filter portion can comprise a filtermaterial which filters the signals. The filter material can be the sameor different than the material for the substrate 104. For instance, inone embodiment, the filter portion comprises a portion of the substrate104 surrounding and/or adjacent to the signal line 102, and the portioncan be loaded with frequency absorbing particles to provide a desiredfiltering effect to signals on the signal line 102. In some embodiments,the substrate 104 can be loaded with frequency absorbing particles toprovide the filtering effect.

In some embodiments, a cavity can be formed within the substrate 104which can be filled with a filter material different than the substrate104. For instance, the dielectric portion can be formed of a firstpolymer. The frequency absorbent material can include frequencyabsorbing particles embedded within a second polymer (e.g., a curablepolymer) that is different than the first polymer. As one example, acavity can be filled with the curable polymer wen the curable polymer isin an uncured state.

Generally, the cavity can be formed according to any suitable approach.For instance, the cavity can be formed by removal of material within thesubstrate 104. However, it is also contemplated that the cavity could beformed by the selective omission of substrate 104 in areas in which afilter material is intended to be placed. For example, the substrate 104could be formed in layers, as noted above, and one or more of the layerscould include voids which, when joined with adjacent layers, provides acavity within the substrate 104 that may be filled with a filtermaterial. In some embodiments, the substrate 104 could be formed usingadditive manufacturing techniques, and one or more portions of thesubstrate 104 could selectively not be added during the manufacturing,forming a cavity thereby.

In some embodiments, a cavity can be formed in the substrate 104 byprocessing an existing laminated circuit assembly. For instance, in FIG.3, a laminated circuit assembly 100 is depicted which can be processedaccording to example aspects of the present disclosure. In someembodiments, the processing can include removing a portion of one ormore layers of material which may be laminated to the substrate 104. Forinstance, in FIG. 4, the laminated circuit assembly 100 is depicted witha portion of the planar conductor 106 a removed, exposing an area 108 ofthe substrate 104. Although FIG. 4 depicts the area 108 being exposed asrectangular, it is to be understood that the exposed area 108 can assumesubstantially any form, and, because some embodiments may lack a planarconductor 106 a, the exposed area 108 may take substantially the form ofthe surface of the substrate 104. The exposed area 108 can provide anaccess for removing material from the substrate 104.

In some embodiments, the processing can include removing a portion ofthe substrate 104 to form a cavity which may be partially or completelyfilled with a filter material. For instance, FIG. 5 depicts thelaminated circuit assembly 100 which has had a portion of the substrate104 removed along a length 110, width 112, and depth 114.

In some embodiments, portions of the substrate 104 can be removed bycutting, drilling, milling, abrading, or otherwise mechanically removed.In some embodiments, portions of the substrate 104 can be removed byetching or other chemically reactive material removal processes. In someembodiments, portions of the substrate 104 can be removed by ablation toform the cavity (e.g., laser ablation, etc.). For example, as shown inFIG. 5, material may be removed from the substrate 104 from onedirection (e.g., from they-direction, as shown). For instance, materialfrom the substrate 104 can be selectively removed from above the signalline 102 in the y-direction and from beside the signal line 102 in thez-direction. In some examples, depending on the material removal method,the composition of the signal line 102 and/or coatings thereon caninfluence the selective removal of material. For instance, in someembodiments, the material(s) of the signal line 102 may be resistive tothe removal process (or, at least more resistive than the surroundingmaterial of the substrate 104). In this manner, a material removalprocess can be applied over the area covered by the length 110 and thewidth 112 without masking the area above the signal line 102. Forinstance, a material of a signal line 102 can be resistive to anablation process, such that the area covered by length 110 and width 112can be ablated without masking the area above the signal line 102. Inthis manner, the speed and throughput of the ablation process(es) can beimproved.

After the material of the substrate 104 is removed, the cavity formedthereby can be filled with a filter material to form a filter portion116 of the substrate 104, as depicted in FIG. 6. The filter portion 116can be completely filled, as shown in FIG. 1D, or, in some examples, bepartially filled. For instance, the filter portion 116 can be filledwith a first filter material and a second filter material, each filtermaterial partially filling the cavity. In some embodiments, a filtermaterial can partially fill the cavity (e.g., a portion of the cavitydirectly surrounding the signal line 102) and another material (e.g.,the material of substrate 104) could be filled in the remaining portionof the cavity to encapsulate the filter material. The filter portion 116can extend to a surface of the substrate 104 and/or extend to the outersurface of a planar conductor laminated to the substrate 104 (e.g., asshown in FIG. 6).

FIG. 7 depicts a cross-sectional view of the filter portion 116 withinthe substrate 104. The filter portion 116 can assume substantially anyshape defined by one or more boundaries of the cavity formed within thesubstrate 104. For instance, one boundary may be defined based on thedepth 118 of the signal line 102 within the substrate 104. Anotherboundary may be configured to extend the legs of the filter portion 116an additional depth 120 to surround the signal line 102, such that thelegs can cover the thickness 122 of the signal line 102 plus anotherdistance 124 beyond the thickness 122 of the signal line 102. In thismanner, the filter portion 116 can at least partially surround thesignal line 102 to provide filtration to one or more signals travellingalong the signal line 102. Additionally, the width 112 of the cavity canbe configured such that the filter portion 116 can extend a distance 126on one or both sides of the signal line 102 beyond the width 128 of thesignal line 102. In some examples, the filter portion 116 extends atleast a distance 126 on both sides of the signal line 102, but canoptionally extend a distance longer than distances 126 on one side ofthe signal line 102 to provide additional filtering and/or shielding onthe one side (e.g., to reduce crosstalk and/or other interference fromanother signal line near that one side).

Although the preceding description has referred to figures which depicta cavity being formed which exposes the signal line 102, it iscontemplated that a cavity according to other example aspects of thepresent disclosure can be formed which does not expose the signal line102. For instance, it may be desired, in some cases, to form a cavity inone process (e.g., with one set of equipment) and transfer the processedsubstrate 104 to another system for further processing. In oneembodiment, it may be desired that at least some substrate materialremain to protect and/or shield the signal line 102 from damage and/orcontamination. For example, in some embodiments, the filter material ofthe filter portion may exert mechanical stresses on the signal line 102when the filter material is filling the cavity (e.g., during insertionand/or injection, during adhering of the filter material and/or duringcuring of the filter material, etc.). It may be desirable, in somecircumstances, for at least some of the substrate material of thesubstrate 104 to remain as a support for the signal line.

For example, FIG. 8 depicts a cross-sectional view of a circuit assembly200 having another profile of a filter portion 116 which does not extendto the signal line 102 but is instead separated a distance 230 from thetop of the signal line 102. Similarly, in some embodiments, the legs ofthe filter portion 116 can be spaced apart a distance 232, which may begreater than the width 128 of the signal line 102, to leave some of thematerial of substrate 104 surrounding the signal line 102.

Although the preceding description has referred to figures which depictmaterial from the substrate 104 being removed from one side of thesubstrate (e.g., one outer surface), it is contemplated that materialcan be removed from both sides (e.g., above and below the signal line102 in the y-direction). For instance, FIG. 9 depicts a circuit assembly250 having another profile of a filter portion 116. A cavity within thesubstrate 104 can be formed which divides the substrate 104 into twoportions 104 a and 104 b (at least on the viewing plane depicted; theportions 104 a and 104 b may, in some embodiments, be connected out ofview). The cavity can, in some embodiments, be formed by removingmaterial from both sides of the circuit assembly 250 (e.g., by removingan area of the planar conductor 106 a, if present, and/or by removing anarea of the planar conductor 106 b, if present). In this manner, asubstantially symmetric cavity can be formed (e.g., reflectivelysymmetric about the signal line 102).

In some embodiments, the cavity can extend to one or more (e.g., all)surfaces of the signal line 102, such that no substrate material fromthe substrate 104 remains within the filter portion 116 (e.g., as shownin the circuit assembly 400 of FIG. 10, with the cavity extending depths118 a and 118 b to abut the signal line 102). In some embodiments,however, such as shown in FIG. 9, dielectric supports 256 a and 256 bcan be provided (e.g., substrate material not removed). The dielectricsupports 256 a and 256 b can be respectively configured to be the sameor different (e.g., support heights 256 a and 256 b can be the same ordifferent). In this manner, support can be provided for the signal line102 to support the signal line during subsequent processing (e.g., thefilling of the filter portion 116 with filter material, etc.).Dielectric supports 256 a and 256 b can include a portion of adielectric not removed during formation of a cavity.

FIG. 9 also depicts covers 258 a and 358 b which can be used to coverthe accesses used to form the cavity within the substrate 104. One orboth of the covers 258 a and 258 b can comprise a conductive material.In one embodiment, the covers 258 a and 258 b are comprised within aplanar conductor 106 a and 106 b, respectively (e.g., a planar conductor106 a and/or 106 b can be laminated to the substrate 104 after formationof the filter portion 116). In some embodiments, another conductor(e.g., another planar conductor) can be applied or laminated over theaccess(es) to form at least one of the covers 258 a and 358 b. Forinstance, a conductive paint or other coating can be applied. Theconductive coating can dry and/or cure in place to provide one or bothof covers 358 a and 358 b.

In some embodiments, any one, subset, or all of the communicationsdescribed above can be communicated via one or more signals travelingalong a filtered signal line 102 described herein according to exampleaspects of the present disclosure. For instance, in one embodiment, afiltered signal line 102 according to example aspects of the presentdisclosure can be used to communicate qubit interface signals from acontrol device for controlling and/or reading the behavior of one ormore qubits. For example, in one embodiment, the signal line 102 can beused to communicate one or more signals associated with a Pauli X, Y,and/or Z operator.

In one embodiment, a quantum computing system comprises a qubit and asignal line 102 associated with the qubit. The signal line 102 and qubitmay be configured and arranged such that, during operation of thequantum computing device, the signal line 102 allows coupling of an XYqubit control flux bias over a first frequency range. The signal line102 can also provide for the coupling of a Z qubit control flux biasover a second frequency range. In some embodiments, the attenuation ofthe signal(s) traveling along the signal line 102 can be configured toavoid excess joule heating contributed by excess attenuation of thesignals in different frequency ranges. For instance, the filter portion116 dimensions and/or the filter material can be configured such thatthe filter portion 116 can include a frequency absorbing materialproviding less attenuation to signals of a first frequency and greaterattenuation to signals of a second, different frequency (e.g., which maybe higher or lower). For instance, some filter materials provideattenuation that increases in a substantially monotonic fashion withincreasing signal frequency for at least a portion of a targetedfrequency band.

In some embodiments, aspects of the filter material can be configuredfor lowpass and/or bandpass operation. For example, in one embodiment,the filter portion 116 may be configured to attenuate at a firstattenuation level in the 0 to 0.5 GHz frequency band and attenuate at asecond attenuation level in the 2 to 8 GHz frequency band. While the XYcontrol signals can be operating in the microwave frequency band, insome cases, the Z control signals (which, in some examples, can behigher-power signals than the XY control signals), however, can operatein the 0 to 0.5 GHz band, in some cases. Excessively attenuating the Zqubit control signal may lead to substantial joule heating within theattenuator. The heating, in turn, may increase noise and render itdifficult to maintain the low temperature that may be necessary toprovide superconducting operation of circuit elements of qubit. Forinstance, the joule heating may unduly burden or exceed the coolingpower of a cryostat or cryostat stage in which the qubit is operating.In some embodiments, the filter portion 116 can be configured toattenuate signals greater than about 10 GHz at a level of attenuationgreater than the attenuation provided to the 0 to 0.5 GHz frequency bandand the 2 to 8 GHz frequency band, so as to attenuate thermal radiation(e.g., infrared signals) passing through and/or traveling along thesignal line.

FIG. 11 depicts a flow chart diagram of an example method 600 accordingto example embodiments of the present disclosure. FIG. 11 depicts stepsperformed in a particular order for purposes of illustration anddiscussion. Those of ordinary skill in the art, using the disclosuresprovided herein, will understand that various steps of any of themethods disclosed herein can be adapted, modified, performedsimultaneously, omitted, include steps not illustrated, rearranged,and/or expanded in various ways without deviating from the scope of thepresent disclosure.

At 602, the method can include receiving or obtaining a laminatedcircuit assembly. The laminated circuit assembly can be constructedaccording to any of the example embodiments disclosed herein. Thelaminated circuit assembly can include one or more signal lines disposedin a first direction within a dielectric material of a substrate. Thelaminated circuit assembly can define a second direction normal to thesubstrate and a third direction that is orthogonal to the firstdirection and the second direction.

At 604, the method can include forming a cavity within the substrate byremoving a portion of the dielectric material above the signal line inthe second direction. The cavity can extend in the first direction alongthe signal line.

At 606, the method can include filling the cavity with a frequencyabsorbent material. The frequency absorbent material can be configuredaccording to any of the embodiments disclosed herein. The frequencyabsorbent material can provide less attenuation to a first signal for afirst frequency than to a second signal of a second, higher frequency.The filled cavity can be configured to attenuate infrared signalspassing through the one or more signal lines.

Additional Disclosure

Implementations of the digital and/or quantum subject matter and thedigital functional operations and quantum operations described in thisspecification can be implemented in digital electronic circuitry,suitable quantum circuitry or, more generally, quantum computationalsystems, in tangibly-implemented digital and/or quantum computersoftware or firmware, in digital and/or quantum computer hardware,including the structures disclosed in this specification and theirstructural equivalents, or in combinations of one or more of them. Theterm “quantum computational systems” may include, but is not limited to,quantum computers/computing systems, quantum information processingsystems, quantum cryptography systems, or quantum simulators.

Implementations of the digital and/or quantum subject matter describedin this specification can be implemented as one or more digital and/orquantum computer programs, i.e., one or more modules of digital and/orquantum computer program instructions encoded on a tangiblenon-transitory storage medium for execution by, or to control theoperation of, data processing apparatus. The digital and/or quantumcomputer storage medium can be a machine-readable storage device, amachine-readable storage substrate, a random or serial access memorydevice, one or more qubits/qubit structures, or a combination of one ormore of them. Alternatively or in addition, the program instructions canbe encoded on an artificially-generated propagated signal that iscapable of encoding digital and/or quantum information (e.g., amachine-generated electrical, optical, or electromagnetic signal) thatis generated to encode digital and/or quantum information fortransmission to suitable receiver apparatus for execution by a dataprocessing apparatus.

The terms quantum information and quantum data refer to information ordata that is carried by, held, or stored in quantum systems, where thesmallest non-trivial system is a qubit, i.e., a system that defines theunit of quantum information. It is understood that the term “qubit”encompasses all quantum systems that may be suitably approximated as atwo-level system in the corresponding context. Such quantum systems mayinclude multi-level systems, e.g., with two or more levels. By way ofexample, such systems can include atoms, electrons, photons, ions orsuperconducting qubits. In many implementations the computational basisstates are identified with the ground and first excited states, howeverit is understood that other setups where the computational states areidentified with higher level excited states are possible.

The term “data processing apparatus” refers to digital and/or quantumdata processing hardware and encompasses all kinds of apparatus,devices, and machines for processing digital and/or quantum data,including by way of example a programmable digital processor, aprogrammable quantum processor, a digital computer, a quantum computer,or multiple digital and quantum processors or computers, andcombinations thereof. The apparatus can also be, or further include,special purpose logic circuitry, e.g., an FPGA (field programmable gatearray), or an ASIC (application-specific integrated circuit), or aquantum simulator, i.e., a quantum data processing apparatus that isdesigned to simulate or produce information about a specific quantumsystem. In particular, a quantum simulator is a special purpose quantumcomputer that does not have the capability to perform universal quantumcomputation. The apparatus can optionally include, in addition tohardware, code that creates an execution environment for digital and/orquantum computer programs, e.g., code that constitutes processorfirmware, a protocol stack, a database management system, an operatingsystem, or a combination of one or more of them.

A digital computer program, which may also be referred to or describedas a program, software, a software application, a module, a softwaremodule, a script, or code, can be written in any form of programminglanguage, including compiled or interpreted languages, or declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a digital computing environment. A quantum computerprogram, which may also be referred to or described as a program,software, a software application, a module, a software module, a script,or code, can be written in any form of programming language, includingcompiled or interpreted languages, or declarative or procedurallanguages, and translated into a suitable quantum programming language,or can be written in a quantum programming language, e.g., QCL orQuipper.

A digital and/or quantum computer program may, but need not, correspondto a file in a file system. A program can be stored in a portion of afile that holds other programs or data, e.g., one or more scripts storedin a markup language document, in a single file dedicated to the programin question, or in multiple coordinated files, e.g., files that storeone or more modules, sub-programs, or portions of code. A digital and/orquantum computer program can be deployed to be executed on one digitalor one quantum computer or on multiple digital and/or quantum computersthat are located at one site or distributed across multiple sites andinterconnected by a digital and/or quantum data communication network. Aquantum data communication network is understood to be a network thatmay transmit quantum data using quantum systems, e.g. qubits. Generally,a digital data communication network cannot transmit quantum data,however a quantum data communication network may transmit both quantumdata and digital data.

The processes and logic flows described in this specification can beperformed by one or more programmable digital and/or quantum computers,operating with one or more digital and/or quantum processors, asappropriate, executing one or more digital and/or quantum computerprograms to perform functions by operating on input digital and quantumdata and generating output. The processes and logic flows can also beperformed by, and apparatus can also be implemented as, special purposelogic circuitry, e.g., an FPGA or an ASIC, or a quantum simulator, or bya combination of special purpose logic circuitry or quantum simulatorsand one or more programmed digital and/or quantum computers.

For a system of one or more digital and/or quantum computers to be“configured to” perform particular operations or actions means that thesystem has installed on it software, firmware, hardware, or acombination of them that in operation cause the system to perform theoperations or actions. For one or more digital and/or quantum computerprograms to be configured to perform particular operations or actionsmeans that the one or more programs include instructions that, whenexecuted by digital and/or quantum data processing apparatus, cause theapparatus to perform the operations or actions. A quantum computer mayreceive instructions from a digital computer that, when executed by thequantum computing apparatus, cause the apparatus to perform theoperations or actions.

Digital and/or quantum computers suitable for the execution of a digitaland/or quantum computer program can be based on general or specialpurpose digital and/or quantum microprocessors or both, or any otherkind of central digital and/or quantum processing unit. Generally, acentral digital and/or quantum processing unit will receive instructionsand digital and/or quantum data from a read-only memory, or a randomaccess memory, or quantum systems suitable for transmitting quantumdata, e.g. photons, or combinations thereof.

Some example elements of a digital and/or quantum computer are a centralprocessing unit for performing or executing instructions and one or morememory devices for storing instructions and digital and/or quantum data.The central processing unit and the memory can be supplemented by, orincorporated in, special purpose logic circuitry or quantum simulators.Generally, a digital and/or quantum computer will also include, or beoperatively coupled to receive digital and/or quantum data from ortransfer digital and/or quantum data to, or both, one or more massstorage devices for storing digital and/or quantum data, e.g., magnetic,magneto-optical disks, or optical disks, or quantum systems suitable forstoring quantum information. However, a digital and/or quantum computerneed not have such devices.

Digital and/or quantum computer-readable media suitable for storingdigital and/or quantum computer program instructions and digital and/orquantum data include all forms of non-volatile digital and/or quantummemory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto-optical disks; and CD-ROM and DVD-ROM disks; and quantumsystems, e.g., trapped atoms or electrons. It is understood that quantummemories are devices that can store quantum data for a long time withhigh fidelity and efficiency, e.g., light-matter interfaces where lightis used for transmission and matter for storing and preserving thequantum features of quantum data such as superposition or quantumcoherence.

Control of the various systems described in this specification, orportions of them, can be implemented in a digital and/or quantumcomputer program product that includes instructions that are stored onone or more non-transitory machine-readable storage media, and that areexecutable on one or more digital and/or quantum processing devices. Thesystems described in this specification, or portions of them, can eachbe implemented as an apparatus, method, or electronic system that mayinclude one or more digital and/or quantum processing devices and memoryto store executable instructions to perform the operations described inthis specification.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of what may beclaimed, but rather as descriptions of features that may be specific toparticular implementations. Certain features that are described in thisspecification in the context of separate implementations can also beimplemented in combination in a single implementation. Conversely,various features that are described in the context of a singleimplementation can also be implemented in multiple implementationsseparately or in any suitable sub combination. Moreover, althoughfeatures may be described above as acting in certain combinations andeven initially claimed as such, one or more features from a claimedcombination can in some cases be excised from the combination, and theclaimed combination may be directed to a sub-combination or variation ofa sub-combination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various system modulesand components in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

Particular implementations of the subject matter have been described.Other implementations are within the scope of the following claims. Forexample, the actions recited in the claims can be performed in adifferent order and still achieve desirable results. As one example, theprocesses depicted in the accompanying figures do not necessarilyrequire the particular order shown, or sequential order, to achievedesirable results. In some cases, multitasking and parallel processingmay be advantageous.

What is claimed is:
 1. A laminated circuit assembly, comprising: one ormore signal lines disposed within a substrate in a first direction; adielectric portion of the substrate; and a filter portion of thesubstrate extending in the first direction and containing a frequencyabsorbent material providing less attenuation to a first signal of afirst frequency than to a second signal of a second, higher frequency;wherein the filter portion is configured to attenuate infrared signalspassing through the one or more signal lines.
 2. The laminated circuitassembly of claim 1, wherein: the one or more signal lines areconfigured to transmit control signals from a classical computing deviceto a quantum hardware.
 3. The laminated circuit assembly of claim 1,wherein the dielectric portion is formed of a polymer, and wherein thefilter portion comprises frequency absorbing particles embedded withinthe polymer.
 4. The laminated circuit assembly of claim 1, wherein thedielectric portion is formed of a first polymer, and wherein thefrequency absorbent material comprises frequency absorbing particlesembedded within a second polymer that is different than the firstpolymer.
 5. The laminated circuit assembly of claim 4, wherein thefilter portion comprises boundaries defined by a cavity formed withinthe first polymer of the at least one dielectric, the cavity beingformed by removal of the first polymer and at least partially filledwith the frequency absorbent material.
 6. The laminated circuit assemblyof claim 5, wherein: a second direction is normal to the substrate and athird direction is orthogonal to the first direction and the seconddirection; and a first portion of the cavity is located above the signalline along the second direction, and a second portion of the cavity islocated beside the signal line along the third direction.
 7. Thelaminated circuit assembly of claim 6, wherein the first portion of thecavity extends from an outer surface of the substrate to the signalline.
 8. The laminated circuit assembly of claim 6, comprising: adielectric support supporting the signal line, the dielectric supportcomprising a portion of the at least one dielectric not removed duringformation of the cavity; wherein a third portion of the cavity islocated below the signal line along the second direction.
 9. Thelaminated circuit assembly of claim 6, comprising: a first conductivelayer laminated to an outer surface of the substrate, the firstconductive layer comprising an access for the filling of the cavity withthe frequency absorbent material; and a second conductive layer coveringthe access.
 10. The laminated circuit assembly of claim 9, wherein thesecond conductive layer comprises a curable nonmetallic matrix.
 11. Thelaminated circuit assembly of claim 5, wherein the second polymer is acurable polymer, the cavity having been at least partially filled withthe frequency absorbent material with the second polymer in an uncuredstate.
 12. The laminated circuit assembly of claim 1, wherein the one ormore signal lines comprise: a first signal line having a first filterportion corresponding thereto; and a second adjacent signal line havinga second filter portion corresponding thereto; wherein the first filterportion and the second filter portion are offset from each other in thefirst direction.
 13. The laminated circuit assembly of claim 1, whereinthe filter portion is configured to attenuate signals in at least one ofthe one or more signal lines by at least about 0.5 dB/GHz.
 14. Thelaminated circuit assembly of claim 5, wherein the cavity is formed byablation of the dielectric.
 15. The laminated circuit assembly of claim1, wherein the first frequency is less than about 500 MHz and the secondfrequency is greater than about 2 GHz and less than about 8 GHz, andwherein frequency absorbent material provides greater attenuation to theinfrared signals than to either of the first signal or the secondsignal.
 16. A method for manufacturing a filter for a signal line,comprising receiving a laminated circuit assembly comprising one or moresignal lines disposed in a first direction within a dielectric materialof a substrate, wherein a second direction is normal to the substrateand a third direction is orthogonal to the first direction and thesecond direction; forming a cavity within the substrate by removing aportion of the dielectric material above the signal line in the seconddirection, the cavity extending in the first direction along the signalline; and filling the cavity with a frequency absorbent material,wherein the frequency absorbent material provides less attenuation to afirst signal of a first frequency than to a second signal of a second,higher frequency, wherein the filled cavity is configured to attenuateinfrared signals passing through the one or more signal lines.
 17. Themethod of claim 16, wherein the cavity is formed by ablation of thedielectric material.
 18. The method of claim 16, further comprising:laminating a conductive layer to an outer surface of the substrate, theconductive layer covering an access for the filling of the cavity withthe frequency absorbent material.
 19. A cryogenic cooling system,comprising: a plurality of cooling stages configured to cool a cooledportion of a computing system to a temperature of less than about 3Kelvin; one or more signal lines coupling a control unit to the cooledportion of the computing system; and a laminated circuit assembly,comprising: one or more signal lines disposed within a substrate in afirst direction; a dielectric portion of the substrate; and a filterportion of the substrate extending in the first direction and containinga frequency absorbent material providing less attenuation to a firstsignal of a first frequency than to a second signal of a second, higherfrequency; wherein the filter portion is configured to attenuateinfrared signals passing through the one or more signal lines.
 20. Thecryogenic cooling system of claim 19, wherein one or more of theplurality of cooling stages is configured to providing cooling to atemperature of less than about 20 milliKelvin and comprises thelaminated circuit assembly.